Effect of Filler Wire Feed Rate on the Formation of Porosity in Laser Welded Joints of Magnesium Alloy AZ31B–H24

Abstract

In this work, the effect of a filler wire feed rate was studied with special attention to the proportion of porosity volume in the weld metal, microstructure, and mechanical properties. Butt laser weld joints were created using the Nd:YAG laser. Weld joints were produced with the AZ31 filler wire with a diameter of 1.2 mm. Decreasing the filler wire feed rate of the filler wire led to an increase in the porosity of the weld metal. Therefore, porosity is more likely to occur in laser welding without the use of a filler wire. Clear segregation of aluminium, manganese, and zinc was observed in the EDS maps and the local EDS line profile measurements. The precipitates formed were rich in Al and Mn or Al and Zn, compared to the matrix. They also show a large decrease in Mg content to minimum values ranging from 10 to 60 wt.% in the precipitates. To investigate pores in the weld metal of the weld joint, computed tomography was used. The highest volume of porosity was measured in weld joint no. 3. (0.63 mm3). On the contrary, the lowest porosity volume was detected in weld joint no. 1. (0.06 mm3). The largest width of the weld metal (2.25 mm) was measured if the filler wire feed rate was 130 cm/min. The highest average microhardness (82.5 HV0.1) was recorded in the weld metal of weld joint no. 1. In weld joint no. 3, a fracture occurred in the weld metal and the measured tensile strength was only 154 MPa.